Square balers are used to harvest agricultural crops like hay, silage, or straw. The square baler is pulled by a tractor and mechanically driven by a PTO shaft. The crop is usually precompacted in a precompression chamber and then pressed against the already existing bale by a reciprocally acting plunger in the slightly convergent main bale chamber.
To operate the baler with maximum productivity, a speed of travel may be adjusted in dependence on the size and density of the windrow. In the prior art, various manufacturers have offered control systems that regulate the forward speed of the tractor on the basis of a sensor signal from the square baler. The sensor signal is generated by a sensor integrated into the pickup, precompression chamber, or main bale chamber, and represents a characteristic value for the load of the baler. Many such sensors are known in the prior art (e.g., U.S. Pat. No. 6,546,705 B2). For example, the torque or rotary speed at the pickup, forces on the packers or plunger, or even the number of plunger strokes per new flake are sensed. The disadvantage of these control systems is that they can only operate reactively and, therefore, cannot react to larger variations in the windrow or can react only with a delay. This can result in problems, in particular, when baling straw, which is chopped beforehand by a combine harvester and laid in the windrow. If the combine harvester needs to stop for any reason, a large amount of straw will collect at a single point due to the delayed straw deposition. The driver must actively intervene in such situations, stop the system, and manually drive over the heap of straw. Otherwise, he risks plugging the baler.
To solve this problem, it was proposed to detect and characterize the windrow in front of the tractor by means of sensor technology. This can take place, for example, by means of a (stereo) camera (e.g., U.S. Pat. No. 7,400,957 B2), laser scanner (e.g., U.S. Pat. No. 6,389,785 B1), or ultrasound sensors (e.g., L. Hofmann, “Windrow Scanning with Ultrasound,” Landtechnik 5, 1993, pp. 266-268).
The cost-intensive sensor expense and susceptibilities to environmental effects like dust and dirt have prevented broad commercial use of such predictive systems up to now. It is also disadvantageous with conventional sensor detection of the windrow that only geometric data about the windrow, such as the width, height, cross-sectional area, or volume, can be determined. However, the windrow density and possibly moisture level are likewise relevant for optimum baler throughput control.
The problem of speed optimization also exists with round balers (e.g., German Patent Application No. 102005029405 A1).
European Patent Application No. 2952081 A1 describes a procedure in which various data about the straw are stored during the harvesting of grain (for example, the position of the windrow and the direction of travel of the combine harvester as it was being produced), and the data is used to plan the path of the baler for picking up the windrow, so that the baler can travel in the opposite direction from the direction of the combine harvester. It was further proposed to steer a baler by means of a stored windrow position (e.g., U.S. Patent Application Publication No. 2007/175198 A1, German Patent Application No. 102005047306 A1, German Patent Application No. 102005004508 A1, European Patent Application No. 2267567 A2). The above problem of speed control, however, is not solved by these measures.
Therefore, there exists a need in the art for developing an inexpensive and robust throughput control system for balers that can handle large variations in the windrow.